CSF Cytology Identifies Mechanisms of Tyrosine Kinase Inhibitor Resistance in Patient With EGFR-Mutated NSCLC With CNS Progression

•The traditional assumption that CNS progression in NSCLC patients on TKIs is secondary to lower drug exposure may not always be true; progression may represent biological rather than pharmacological mechanism of resistance.•The current case study suggests that CSF cytology and FISH analysis can be helpful in identification of mechanisms of resistance in CNS progression and guide treatment decisions.